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Molecular and Cellular Biology, March 2000, p. 2209-2217, Vol. 20, No. 6
Department of Biochemistry, University of
Nijmegen, 6500 HB Nijmegen, The Netherlands,1
and Department of Molecular Biology and Biochemistry,
Rutgers University, Piscataway, New Jersey 088552
Received 5 October 1999/Returned for modification 9 November
1999/Accepted 9 December 1999
It was previously shown that the human U1A protein, one of three U1
small nuclear ribonucleoprotein-specific proteins, autoregulates its
own production by binding to and inhibiting the polyadenylation of its
own pre-mRNA. The U1A autoregulatory complex requires two molecules of
U1A protein to cooperatively bind a 50-nucleotide polyadenylation-inhibitory element (PIE) RNA located in the U1A 3'
untranslated region. Based on both biochemical and nuclear magnetic
resonance structural data, it was predicted that protein-protein interactions between the N-terminal regions (amino acids [aa] 1 to
115) of the two U1A proteins would form the basis for cooperative binding to PIE RNA and for inhibition of polyadenylation. In this study, we not only experimentally confirmed these predictions but
discovered some unexpected features of how the U1A autoregulatory complex functions. We found that the U1A protein homodimerizes in the
yeast two-hybrid system even when its ability to bind RNA is
incapacitated. U1A dimerization requires two separate regions, both
located in the N-terminal 115 residues. Using both coselection and gel
mobility shift assays, U1A dimerization was also observed in vitro and
found to depend on the same two regions that were found in vivo.
Mutation of the second homodimerization region (aa 103 to 115) also
resulted in loss of inhibition of polyadenylation and loss of
cooperative binding of two U1A protein molecules to PIE RNA. This same
mutation had no effect on the binding of one U1A protein molecule to
PIE RNA. A peptide containing two copies of aa 103 to 115 is a potent
inhibitor of polyadenylation. Based on these data, a model of the U1A
autoregulatory complex is presented.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Fourteen Residues of the U1 snRNP-Specific U1A Protein Are
Required for Homodimerization, Cooperative RNA Binding, and
Inhibition of Polyadenylation
*
Corresponding author. Mailing address: Department of
Molecular Biology and Biochemistry, Rutgers University, 604 Allison
Rd., Nelson Lab, Piscataway, NJ 08855. Phone: (732) 445-1016. Fax: (732) 445-4213. E-mail: gunderson{at}biology.rutgers.edu.
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